Male elephant seal - This bull elephant seal is carrying a tag which allows researchers to follow his movements in real-time. The tag is glued to the fur, which is molted each year.

Photo: Photo Courtesy Of TOPP

Male elephant seal - This bull elephant seal is carrying a tag...

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Tagged white shark - This white shark, photographed at the Farallon Islands off Northern California, has been tagged with an acoustic tag (front) and a pop-up satellite tag (rear) as part of the TOPP research program.

Tagged elephant seal - This female elephant seal is carrying a tag which allows researchers to follow her movements in real-time. The tag is glued to the fur, which is molted each year.

Photo: Photo Courtesy Of TOPP

Tagged elephant seal - This female elephant seal is carrying a tag...

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Tagged Laysan Albatross - Laysan albatross, tagged in the Northwest Hawaiian Islands, can be followed in real-time, thanks to small, lightweight satellite tags which are attached to the feathers on their back.

Pacific bluefin tuna - Pacific bluefin tuna are the super-athletes of the ocean. TOPP researchers followed several of them to migrate all the way across the Pacific basin, from California to Japan and back again in a matter of months.

SAN FRANCISCO -- Two broad ocean highways where countless sea creatures migrate, feed, mate and reproduce have been discovered running across the Pacific by scientists tuning in to thousands of radio signals.

The calls have come from electronic tags fitted to the Pacific's top predators - sharks and whales and the wandering albatross, for example. In all, the 23 most important of those creatures - in the water and the air - have revealed a far more complete picture of the behavior patterns and environments of the ocean's animals than the fragmentary information known before to science.

The discovery of the two highways is the culmination of a wide-ranging 10-year project involving more than 75 scientists from five nations, including the project's leaders, Barbara Block of Stanford's Hopkins Marine Station and Daniel Costa of UC Santa Cruz.

The scientists call the highways "the corridors of life" and "the grasslands of the sea," and likened them to Africa's vast Serengeti Plain, where countless species of African land animals live and migrate. The ocean regions are major habitats for the Pacific's predators and their victims lower on the food chain - indeed for everything down to the krill and plankton of the ocean's depths.

One is the huge area where the cool, nutrient-rich California Current flows southward from the Arctic along the California and Mexican coast and outward from the near-shore into the deep sea beyond. The other is the broad region known as the North Pacific Transition Zone that crosses from Japan to the coast of Washington.

Twenty-one of the project's leading researchers are reporting their combined results today in the online edition of the journal Nature.

Tracking migrations

The scientists attached 4,306 tags - many of them holding tiny radio transmitters - to more than 3,500 birds and animals, and followed the seasonal migrations of many of them year after year. The signals sent by the radio tags allowed the scientists to locate many hot spots along the highways where each species gathers regularly to feed and reproduce, and to follow them along their migratory routes.

Sensors in many of the tracking tags gave the researchers complex data on the salinity of the so-called highways and on the area's light levels and temperatures.

The major goal of the international project - Tagging of Pacific Predators, or TOPP, as it's called - was to deepen scientific understanding of the Pacific's biodiversity so that threatened species can be protected internationally and productive fisheries can be managed more effectively, the scientists said.

Although the migratory patterns and habitats of some predators have been reported before, Block and Costa said this was the first time the entire ecosystems of the Pacific's two great centers of biodiversity have been understood, they said.

"It pulls all the pieces together," Costa said.

For example, the TOPP report noted that the radio tags show clearly how, when water temperatures are just right, leatherback turtles migrate seasonally from their nesting beaches in Papua, New Guinea, into the California current - many winding up in the waters around the Farallones off of San Francisco.

Shearwaters, long-winged seabirds, reach the California current from New Zealand, and loggerhead turtles migrate annually from Japan, the TOPP project noted.

Tale of two highways

California sea lions live their entire lives inside the California Current, but the TOPP researchers found that elephant seals, sharks, albatrosses, tuna and many other predators migrate and forage in the North Pacific Transition Zone before moving on each year.

One TOPP team scientist, Bruce Mate of Oregon State University, noted that blue whales being tracked off Santa Barbara swiftly left when upwelling died away and the krill the whales were feasting on disappeared. Most of the whales quickly moved to the Farallon Islands, Mate's group found, traveling 400 miles in three days to where the animals apparently knew upwelling there would bring more krill to the surface.

The electronic tags used for the project involved entirely new technologies, according to Costa. Many of the tags were attached to the fur of animals and lost when the animals molted; birds carried miniaturized transmitters like ankle bracelets, while larger fish bore tags harmlessly affixed to their skins.

The TOPP project turned out to be a highly successful advanced proving ground for many new tagging technologies to be used for future ocean research, the researchers noted.